1. Field of the Invention
This invention relates to an ink container and an ink cartridge (an ink container filled with ink) for supplying ink to a stencil printer and to a method of manufacturing the ink cartridge. The invention further relates to an inner plug for a stencil printing ink container.
2. Description of the Related Art
There has been known a stencil printer in which print is made by the use of a heat-sensitive stencil. In such a stencil printer, a stencil is made by, for instance, bringing a thermal head having a plurality of fine heater elements arranged in a row into contact with heat-sensitive stencil material with the heater elements selectively energized according to the image to be printed while the stencil material is conveyed by a platen roller or the like, thereby imagewise perforating the stencil material. The stencil thus made is wound around a printing drum and a printing paper is pressed against the stencil by a pressing member such as a press roller so that ink is transferred to the printing paper through the perforations.
In order to make smaller the diameter of the perforations to obtain fine printed images or to make higher the penetration of the ink into the printing papers to increase the printing speed, it is preferred that the ink be lower in viscosity. Especially, by lowering the viscosity of ink in a region where shear rate is not higher than 100 sec−1, the ink transferred to the printing papers more quickly penetrates into the printing papers and printings free from offset can be obtained.
As a means for supplying ink to the stencil printer, there has been employed a mechanism comprising an ink supply roller which is supported for revolution about its axis by a pair of opposed plate, a distributor which supplies ink onto the ink supply roller and a doctor roller which is disposed spaced from the ink supply roller to control the thickness of ink film formed on the roller. As the distributor, those comprising a tubular member provided with a plurality of small holes or comprising a plurality of nozzles have been known. Ink in an ink container is sucked by an ink pump and is supplied onto the ink supply rollers in the form of drops through the distributor so that an ink fountain is formed in the wedge-like space between the ink supply roller and the doctor roller. Ink in the ink fountain is supplied into the printing drum through the gap between the ink supply roller and the doctor roller. A predetermined amount of ink is constantly held in the ink fountain so that ink can be uniformly supplied.
W/O type emulsion ink containing an oil phase in 10 to 50 wt % and a water phase in 90 to 50 wt % is generally employed in the stencil printer. If the stencil printer is kept unused for a long time, the ink remaining in the ink fountain is exposed to air and the water content therein evaporates, whereby ink high in pigment concentration and accordingly low in viscosity remains in the ink fountain. When new ink is supplied to the ink fountain in which such ink high in pigment concentration and low in viscosity remains, the new ink does not readily mix with the remaining ink and an unevenness in density can occur in the printings. Such an unevenness in density is more serious in ink which is high in viscosity in a region where the shear rate is not higher than 100 sec−1.
As the ink container employed in the stencil printer, there have been known, for instance, an ink container comprising an outer box formed of corrugated board and a flexible inner bag accommodated in the outer box so that an ink discharge pipe formed on one end of the inner bag projecting outside the outer box with the outer end thereof closely sealed with a cap (will be referred to as “a BIC-type ink container”, hereinbelow).
However, the BIC-type ink container is disadvantageous in that if ink which is relatively low in viscosity in the above identified region is charged in the ink container, the ink can be discharged through the ink discharge port (provided on the outer end of the ink discharge pipe) to contaminate user's hand and/or wear, the internal part of the stencil printer, the floor on which the stencil printer is installed and/or the like when the user holds the ink container with the ink discharge port directed downward and the cap removed.
In order to overcome this problem, there has been proposed, in Japanese Unexamined Patent Publication No. 2000-318288 (will be referred to as “patent publication 1”, hereinbelow. ), an ink container provided in the ink discharge port with a valve which is opened in response to loading the ink container onto a printer.
Further, Japanese Unexamined Patent Publication No. 2000-272097 (will be referred to as “patent publication 2”, hereinbelow.) discloses a method of loading an ink container onto a printer in which an ink container is loaded onto a printer with the ink discharge port directed upward so that the user do not direct the ink discharge port downward with the ink discharge port opened.
Further, there has been known an ink container comprising a cylinder provided with an ink discharge port on the front thereof and a piston inserted into the cylinder (will be referred to as “a piston-type ink container”, hereinbelow). The piston-type ink container is advantageous over the BIC-type ink container in that the amount of ink remaining in. the ink container after ink is sucked to the very end is smaller and ink can be effectively used. In this ink container, the ink discharge port is sealed by a cap which is screwed on the ink discharge port. When using the ink container, the cap is unscrewed and the ink container is inserted into the stencil printer from the container holder of the stencil printer so that the ink suction port of the stencil printer is fitted with the ink discharge port of the ink container.
However, the ink container proposed in “patent publication 1” is disadvantageous in that the valve provided in the ink discharge port is apt to be damaged since it is arranged by precise and delicate components, and that the number of components increases to add to the cost.
Further, the method disclosed in “patent publication 2” can only be applied to ink containers of a limited size. Further, the ink container used in the stencil printer is required to accommodate a relatively large volume of ink, 500 ml to 1500 ml, since the stencil printer is suitable for making a relatively large number of copies from one original and the ink container for the stencil printer has been designed on the assumption that a larger amount of ink is consumed in a short time as compared with general office appliances, and accordingly, the method disclosed in “patent publication 2” cannot be satisfactory unless the diameter and/or length of the drum are greatly enlarged.
In ink containers for stencil printers, it is preferred that the ink discharge port be as small as possible in order to prevent ink low in viscosity from dripping from the ink discharge port when mounting the ink container on the stencil printer or removing the ink container from the stencil printer. At the same time, it is necessary for the ink discharge port to be provided with a means for giving the ink suction nozzle of the stencil printer easy access thereto.
On the other hand, it is preferred that the ink charge port of the ink container be as large as possible from the viewpoint of ensuring high charging efficiency.